The possibility of natural and human triggered wind slab and storm slab avalanches is present in steeper terrain, near and above treeline.
Natural and human triggered wet avalanche activity will be possible as the warm weather returns to steep sunny slopes near treeline.
The March 23rd storm deposited ~20+ inches of snow and 2+ inches of snow water equivalent at elevations above 10,000'. Since then strong winds in many directions have stripped new snow and created wind slabs. Because of seasonably cool temperatures near treeline, there may be powder snow available for transport near treeline and new wind slabs are still a possibility. Also, new weather may increase wind slab formation - light snow and strong southwest to west winds are forecasted for today (Friday), switching west, northwest, then north by Saturday.
During the afternoon of March 25th, on northern slopes of Doyle Peak (between Sickle Moon and Telescope Chutes) we observed new wind slabs forming from southern winds. On Sunday morning, March 26th an approximately R2D2 classified avalanche was observed in the Telescope Chute of Doyle Peak, north aspect. This likely released during the evening of March 25th, when the Agassiz Station reported southwestern winds.
After these wind events, more new snow fell overnight from March 27th into the 28th. This produced ~4" of new snow accumulation with winds of 9-14 mph at 11,500'. Pit stability tests identified new wind slabs failing on top of previous graupel layers. This weak layer was found in Snowslide Bowl on a generally east facing aspect at 11,800'. New snow accumulating between March 31st and April 1st may continue the cycle of new slabs forming on weaker layers.
Near and Above Treeline:Last week's storm, graupel events throughout the week, and wind at elevation have produced hard and soft slabs of varying thickness on leeward and cross-loaded slopes. Graupel may be a weak layer. New snow and wind loading may aggravate old wind slabs or create new slabs.
Below Treeline:Watch for isolated terrain-traps at lower elevations where steeper slopes have the potential to produce small avalanches. There is the possibility of new storm slabs forming as well as a general warming trend throughout the week adding to the potential of wet slab releases.
Southerly and westerly aspects below 10,000' are quickly losing snow coverage as springtime warming continues. Rocks and logs are emerging just under the surface and may be hidden by recent snow. As temperatures are still dropping below freezing, north, north east, and north west aspects are retaining snow coverage.
Wind slabs of up to 30cm thick have been observed on NE slopes at 11800' with relative weakness on graupel layers. Exercise cautious route selection on steep slopes with recent wind loading. More loading today and tonight may aggravate these older slabs or create new slabs.
Always keep in mind, wind slabs are unpredictable, and may support the weight of a skier or rider initially, and fail suddenly. Avoid snow surfaces which are recently loaded, sound hollow, have signs of fracturing, cracking, or whoompfing sounds.
Storm slab and wind slab avalanches are possible. These slabs may become more sensitive with added snow accumulation and accompanying wind loading throughout the current storm. These conditions will change as the new slabs are affected by strong solar radiation, and/or rapid changes in air temperature throughout the week.
Warm temperatures return to more sun exposed slopes by Sunday. Eventually warm temperatures will return to all slopes. Watch for deep slush, snowballing, pinwheels, and small wet slough indicating the potential for larger wet sloughs or wet slab releases. Keep an eye on the Agassiz Weather Station which is near treeline. If overnight temperatures do not drop below freezing then wet avalanche hazard will increase near treeline.
Quick warming after new snow can cause wet avalanches. Rain on snow can cause wet avalanches.
This season numerous rescues have been conducted by Coconino County Search and Rescue, and the Arizona Snowbowl Ski Patrol. Some of these could have been avoided by better planning and preparation.
Travelers are advised to exercise caution, make slope specific evaluations and most of all, know where you are going and be prepared for the unexpected.
As always, please treat this summary with appropriately guarded skepticism, make your own assessments, and contribute to our body of knowledge by reporting your observations.
Arizona Snowbowl uphill policy.
During winter, backcountry permits are required to access the Kachina Peaks Wilderness. More info
Last updated on Friday, March 31, 2017
Windy and unsettled weather dominated last week's weather and seems destined to continue. Seasonally average or below average temperatures and unstable weather will continue into the weekend and early next week as several cold low pressure systems pulse through our region interrupted by short-lived high pressure ridging. Approximately 4" of snow fell overnight at mid-mountain elevations.
Four to eight inches of snow (near treeline) is forecasted between now and Saturday morning, April 1st. This will be accompanied by westerly and northwesterly winds, as well as the possibility of thunder and lightning. That's no April fools joke!
After a short break in the action, a second storm is predicted to follow on Monday or Tuesday. Wind rather than precipitation will be the theme for the upcoming week.
The Inner Basin SNOTEL site (Snowslide) reported a snow depth of 67 inches (170 cm) at 9700'. Arizona Snowbowl reported 95 inches (241 cm) at 10800'. Since March 24th SNOTEL temperatures ranged between 20° and 54° F and Agassiz station between 10° and 39° F.
Season snowfall to date is 316" (8 meters) at AZ Snowbowl, 10800'.